Method for Manufacturing Reduced-Weight Paper, Thin Cardboard and Cardboard, and Compounds Obtained Therewith

ABSTRACT

The invention concerns a compound for manufacturing paper or cardboard, comprising a mixture of cellulose fibres and heat-expandable substances suited to generate closed microbubbles, in water dispersion, and wherein the mixture also contains additive substances like bonding agents, mineral fillers, coatin starches.

The present invention concerns a method for preparing compounds for the manufacture of paper or cardboard or thin cardboard both in paper machines on an industrial scale and manually, according to traditional handicraft techniques.

The present invention also concerns the compounds obtained with the above mentioned method.

As is known, the paper usually manufactured both in paper machines and with handicraft techniques consists of fibrous, generally vegetable raw materials, felted together and then dried.

The material that is most commonly used for manufacturing paper is constituted by cellulose fibres obtained from trees or plants in general.

The surface of the raw paper is then covered using a range of additives that form a coat.

The coating agents are generally starch, polyvinyl acetate (PVA) and many other products suitable for making different types of paper.

The paper obtained in this way, however, has some drawbacks.

A drawback is due to the fact that normally the paper produced, when it is bulky, is also rather heavy and difficult to transport.

This is the cause of the excessive weight of books, for example school books, which may damage in particular the backbone when the books are transported in school bags that students carry on their backs.

Similarly, also the documents kept in bags or folders are rather heavy when they are bulky.

A further drawback is due to the fact that paper manufacturing costs are a consequence of the high quantity of cellulose fibres used and of felled trees.

The object of the present invention is to carry out a compound for manufacturing paper and/or cardboard and/or thin cardboard that, considering the same volume produced, greatly reduces its weight and consequently makes it easier to transport for the user.

A further object of the present invention is to carry out a compound that solves the problem of the damage to the backbone due to the excessive weight carried.

It is another, yet not the least object of the invention to carry out a compound that, considering the same volume of paper and/or cardboard and/or thin cardboard to be manufactured, allows a reduced quantity of cellulose fibres to be used for making paper.

The objects mentioned above are achieved by the present invention concerning a compound for the manufacture of paper or cardboard, whose main principles are in accordance with the contents of the first claim, as well as a method for the production of the above mentioned compound.

Advantageously, the compound carried out according to the invention allows the apparent specific weight of copy or printing paper to be reduced from 1.0 to at least 0.5.

Still advantageously, the compound carried out according to the invention allows the paper to be recycled with no need for any separation of the material from which it is made.

Still to advantage, the compound carried out according to the invention allows paper and cardboard to be manufactured that are more elastic and flexible than the paper and cardboard of known type.

According to the present invention, the production of paper and cardboard is achieved by using virgin cellulose fibres and/or fibres recycled before or after use, even if with the addition of suitable auxiliary substances like bonding agents, mineral fillers, starches and coating agents, in combination with a water dispersion of substances that expand when heated and generate closed microbubbles.

The microbubbles that expand when heated, in order to function as expanding agents for the paper panel in the most suitable way, are added to the fibre suspension (that is, the paper pulp) before the addition of the suitable cohesion agents.

Cationic starch in solution has resulted to be particularly suitable and effective.

The cationic starch in solution has been normally employed here before the formation of the fibre panel that takes place on the paper wire.

The dispersion particles that expand when heated, firmly anchored to the constituent parts of the paper panel, were left to rise at the same time as the paper and/or cardboard sheet was dried.

In order to ensure the best possible development of the expanding function in paper, the temperature of the drying cylinders (or of the drying plate, if the paper is handmade) must exceed 110° C. and at such temperatures the contact time of the paper panel, in which also the cellulose bonds form, must be sufficient to ensure the drying of the sheet with at least 88% of dry material.

Some non-limiting examples of formulation of the compound carried out according to the invention are illustrated here below.

EXAMPLE N. 1

Here paper is manufactured using 4% of polymer in the form of expandable thermoplastic microspheres encapsulating a gas, produced by Akzo Nobel and marketed under the Expancel® trademark.

In this case, 20 kg of a dispersion of Expancel® were added to a water dispersion having a dry concentration usually included between 0.4% and 7%, constituted by 100 kg of whitened cellulose obtained from fir, by 280 kg of whitened cellulose obtained from eucalyptus and by 50 kg of micronized calcium carbonate.

35 kg of a water dispersion of diketenic synthetic bonding agent were added to this pulp.

This type of bonding agent makes paper suitable for writing with water inks.

This pulp is always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles.

In order to increase the surface strength characteristics of the paper panel, paper was impregnated in the size press of the paper machine with a 3% dry solution of maize starch.

The manufacturing speed of the paper strip was 50 m/min.

The drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 19% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

EXAMPLE N. 2

Here paper is manufactured using 10% of Expancel®.

In this case, 50 kg of a dispersion of Expancel® were added to a water dispersion constituted by 90 kg of whitened cellulose obtained from fir, by 270 kg of whitened cellulose obtained from eucalyptus and by 40 kg of micronized calcium carbonate.

After homogenizing, obtained by slight agitation of the paper pulp, 35 kg of a water dispersion of diketenic synthetic bonding agent were added, which makes paper suitable for writing with water inks.

This pulp is always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles.

In the paper panel drying and rising stage, the drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

In order to increase the surface strength characteristics of the paper panel, paper was impregnated in the size press of the paper machine with a 3.5% dry solution of maize starch.

The manufacturing speed of the paper strip was 50 m/min.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 35% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

EXAMPLE N. 3

Here paper is manufactured using 20% of Expancel®.

100 kg of Expancel® dispersion consisting of particles having a diameter of a few microns were used.

In this case, the dispersion of Expancel® was added to a water dispersion constituted by 90 kg of whitened cellulose obtained from fir, by 240 kg of whitened cellulose obtained from eucalyptus and by 30 kg of micronized calcium carbonate.

30 kg of a water dispersion of diketenic synthetic bonding agent, which makes paper suitable for writing with water inks, were added to the pulp.

This pulp was always kept under slight agitation and then mixed with 7.5 kg of cationic starch dry solution, with the purpose of obtaining good retention and increasing the number of bonding contacts between fibres, auxiliary substances and expandable bubbles, in particular during the paper panel drying and rising stage.

The manufacturing speed of the paper strip was 50 m/min.

The drying cylinders coinciding with the points of formation of the cellulose bonds were adjusted at a temperature ranging between 115° C. and 125° C.

In order to increase the surface strength characteristics of the paper panel, the paper was impregnated in the size press of the paper machine with a 4% dry solution of maize starch.

It is estimated that a book printed with this paper, with the same format, number of pages and thickness, will weigh 49% less than books manufactured according to the state of the art.

The composition of the pulp is illustrated in Table 1, while the characteristics of the paper produced are illustrated in Table 2.

TABLE 1 Composition of industrial paper pulps. Weight Industrial percentage kg/% reference Example 1 Example 2 Example 3 Whitened fir 100 kg 100 kg  90 kg  90 kg cellulose % 20.3 20.3 18.3 18.1 Whitened eucalyptus 300 kg 280 kg 270 kg 240 kg cellulose % 60.9 56.9 54.8 48.2 Calcium  50 kg  50 kg  40 kg  30 kg carbonate % 10.1 10.1  8.1  6.0 Expancel 0   20 kg  50 kg 100 kg % 0   4.1 10.1 20.1 Bonding agent  35 kg  35 kg  35 kg  30 kg %  7.1  7.1  7.1  6.0 Cationic starch  7.5  7.5  7.5  7.5 %  1.5  1.5  1.5  1.5 Total parts kg 492.5 kg   492.5 Kg   492.5 kg   497.5 kg   % 100.0  100.0  100.0  100.0  Concentration of the 2.5% 3.0% 3.5% 4.0% solution of anionic starch in the size press

TABLE 2 Characteristics of industrial papers Industrial Characteristics reference Example 1 Example 2 Example 3 Thickness-micron % 165 176 185 193 Grams per 150 130 110 90 square metre Apparent 0.910 0.737 0.595 0.466 specific weight Gluing with excellent excellent excellent excellent Pelikan 4001 Offset excellent excellent good moderate printability Copybility good good good good Backprint good excellent good good opacity Mechanical excellent excellent good sufficient workability

EXAMPLE N. 4

In this case the pulp described in Example 1, with the addition of all its constituent parts, was partially used to produce handmade paper sheets.

The fibre suspension was brought to the usual use concentrations, always kept under slight agitation, filtered on the wire of the handmade paper panel according to the traditional manufacturing techniques, pressed and detached from the forming wire, and then transferred onto normal dry felts, and wet-pressed following the usual techniques.

The fibre panel has then assumed such a consistency as to be able to be easily separated from the absorbing agents.

According to the traditional paper manufacturing techniques, the paper or cardboard panel is laid and let to dry in the air at ambient temperature.

In this and in the following examples, in order to allow the thermal expansion of the gases encapsulated in the Expancel® microspheres and to obtain both the rising of the fibre panel and a sufficient cohesion of the constituent parts of the paper panel and of the relevant bonds, the handmade paper sheets, still quite humid (40-70% of water) were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

In these conditions, handmade cellulose sheets were obtained in a few seconds.

The characteristics of the paper produced are illustrated in Table 3.

EXAMPLE N. 5

Also in this case, like in Example 4, the handmade paper sheets, still very humid (40-70% of water), were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

Expanded handmade sheets were produced in this case with the pulp sample of Example 2.

The characteristics of the paper produced are illustrated in Table 3.

EXAMPLE N. 6

Also in this case, like in Examples 4 and 5, the handmade paper sheets, still very humid (40-70% of water) were transferred onto a drying plate with temperature adjusted at 120° C. and provided with a counter-felt exerting a slight pressure.

Expanded handmade sheets were produced in this case with the pulp sample of Example 3.

The characteristics of the paper produced are illustrated in Table 3.

TABLE 3 Composition of handmade paper pulps. Weight Hand percentage making kg/% reference Example 4 Example 5 Example 6 Whitened fir 100 kg  100 kg  90 kg 90 kg cellulose 20.3% 20.3% 18.3% 18.1% Whitened 300 kg  280 kg  270 kg  240 kg  eucalyptus cellulose 60.9% 56.9% 54.8% 48.2% Calcium 50 kg 50 kg 40 kg 30 kg carbonate 10.1% 10.1%  8.1%  6.0% Expancel 0 20 kg 50 kg 100 kg  0  4.1% 10.1% 20.1% Bonding agent 35 kg 35 kg 35 kg 30 kg  7.1%  7.1%  7.1%  6.0% Cationic 7.5 Kg  7.5 Kg  7.5 Kg  7.5 Kg  starch  1.5%  1.5%  1.5%  1.5% Total parts 492.5 kg   492.5 kg   492.5 kg   497.5 kg   100.0%  100.0%  100.0%  100.0% 

TABLE 4 Characteristics of handmade papers Hand making Characteristics reference Example 4 Example 5 Example 6 Thickness-micron % 215 241 292 375 Grams per 150 144 138 122 square metre Apparent 0.70 0.60 0.47 0.32 specific weight Gluing with good good good good Pelikan 4001 Physical- moderate moderate moderate moderate mechanical consistency

The paper obtained according to the examples described has a natural, valuable aspect and is also pleasant to touch.

As an alternative to Expancel®, it will be possible to use other products to generate microbubbles, like Avancell® (copolymers of acrylonitrile) and Micropearl® (copolymers of divinylbenzene).

As colloidal agents it is possible to use cationic agents, anionic agents, non-ionic agents alone or mixed with each other and/or in a different time frequency with colloids and/or retaining and/or fixing agents that at the same time considerably increase the physical-mechanical characteristics of the finished paper panel of papers and cardboards.

An example of a non-ionic agent is polyoxypropylene that, thanks to its high specific weight, allows a considerable quantity of product to be saved when combined with a cationic or anionic agent. 

1) Water dispersion for manufacturing paper or cardboard of reduced specific weight comprising cellulose fibres, thermally expandable thermoplastic microspheres in an amount of 4.1% to 20.1% by weight and a cohesion agent. 2) Water dispersion according to claim 1) characterised in that the cohesion agent is a cationic starch. 3) Water dispersion according to claim 2) characterised in that the cationic starch is present in an amount of 1.5% by weight. 4) Water dispersion according to claim 1) characterised in that it further comprises a bonding agent suitable for making paper writable with water inks. 5) Water dispersion according to claim 4) characterised in that the bonding agent is a diketenic synthetic bonding agent. 6) Water dispersion according to claim 1) characterised in that the cellulose fibres are virgin cellulose fibres and/or recycled cellulose fibres. 7) Water dispersion according to claim 1) characterised in that it further comprises a mineral filler. 8) Paper or cardboard produced with a water dispersion according to claim 1). 9) Method for manufacturing paper or cardboard of reduced specific weight with the following steps: a) preparing a water dispersion of a mixture of cellulose fibres and thermally expandable thermoplastic microspheres in an amount of 4.1% to 20.1% by weight, b) addition of a cohesion agent to the water dispersion, c) drying of the water dispersion to form a a paper or cardboard panel at a temperature above 110° C. 10) Method according to claim 9) characterised in that between step a) and step b) is added a bonding agent suitable for making paper writable with water inks. 11) Method according to claim 9) characterised in that the bonding agent is a diketenic synthetic bonding agent. 12) Method according to claim 9) characterised in that the cohesion agent is a cationic starch. 13) Method according to claim 12) characterised in that the cationic starch is present in an amount of 1.5%. 14) Method according to claim 9) characterised in that the cellulose fibres are virgin cellulose fibres and/or recycled cellulose fibres. 15) Method according to claim 9) characterised in that the water dispersion of step a) further comprises a mineral filler. 16) Method according to claim 9) characterised in that the temperature in step c) lies between 115° C. and 125° C. 17) Use of the water dispersion of claim 1) for manufacturing industrial or handmade paper. 18) Use of thermally expandable thermoplastic microspheres as substitution for cellulose fibres and/or to reduce weight in paper or cardboard. 